Method and apparatus for using resources for device-to-device operation in wireless communication system

ABSTRACT

A method and apparatus for using resources for a device-to-device (D2D) operation in a wireless communication system is provided. A user equipment (UE) receives D2D resources used for transmission of D2D signals in radio resource control (RRC) idle mode, and transmits the D2D signals by using the D2D resources in the RRC idle mode. The D2D resources may be used in the RRC idle mode only, or may be used after entering the RRC connected mode. Alternatively, the UE receives D2D resources used for transmission of D2D signals in RRC connected mode, and transmits the D2D signals by using the D2D resources in the RRC idle mode.

TECHNICAL FIELD

The present invention relates to wireless communications, and morespecifically, to a method and apparatus for using resources for adevice-to-device (D2D) operation in a wireless communication system.

BACKGROUND ART

Universal mobile telecommunications system (UMTS) is a 3^(rd) generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). A long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Recently, there has been a surge of interest in supporting directdevice-to-device (D2D) communication. This new interest is motivated byseveral factors, including the popularity of proximity-based services,driven largely by social networking applications, and the crushing datademands on cellular spectrum, much of which is localized traffic, andthe under-utilization of uplink frequency bands. 3GPP is targeting theavailability of D2D communication in LTE rel-12 to enable LTE become acompetitive broadband communication technology for public safetynetworks, used by first responders. Due to the legacy issues and budgetconstraints, current public safety networks are still mainly based onobsolete 2G technologies while commercial networks are rapidly migratingto LTE. This evolution gap and the desire for enhanced services have ledto global attempts to upgrade existing public safety networks. Comparedto commercial networks, public safety networks have much more stringentservice requirements (e.g., reliability and security) and also requiredirect communication, especially when cellular coverage fails or is notavailable. This essential direct mode feature is currently missing inLTE.

From a technical perspective, exploiting the nature proximity ofcommunicating devices may provide multiple performance benefits. First,D2D user equipments (UEs) may enjoy high data rate and low end-to-enddelay due to the short-range direct communication. Second, it is moreresource-efficient for proximate UEs to communicate directly with eachother, versus routing through an evolved NodeB (eNB) and possibly thecore network. In particular, compared to normal downlink/uplink cellularcommunication, direct communication saves energy and improves radioresource utilization. Third, switching from an infrastructure path to adirect path offloads cellular traffic, alleviating congestion, and thusbenefiting other non-D2D UEs as well. Other benefits may be envisionedsuch as range extension via UE-to-UE relaying.

Radio resources for D2D transmission may be newly defined. The radioresources for D2D transmission may be used according to a radio resourcecontrol (RRC) state of a UE, i.e., RRC idle mode and RRC connected mode.A method for using resources for a D2D operation efficiently isrequired.

SUMMARY OF INVENTION Technical Problem

The present provides a method and apparatus for using resources for adevice-to-device (D2D) operation in a wireless communication system. Thepresent invention provides a method for controlling a D2D operationand/or applicability of D2D resources based on a radio resource control(RRC) state. The present invention provides a method for transmittingD2D signals by using D2D resources, which is received in RRC idle modeor RRC connected mode, in RRC idle mode.

Solution to Problem

In an aspect, a method for using, by a user equipment (UE), resourcesfor a device-to-device (D2D) operation in a wireless communicationsystem is provided. The method includes receiving D2D resources used fortransmission of D2D signals in radio resource control (RRC) idle mode,and transmitting the D2D signals by using the D2D resources in the RRCidle mode.

In another aspect, a user equipment (UE) in a wireless communicationsystem is provided. The UE includes a radio frequency (RF) unit fortransmitting or receiving a radio signal, and a processor coupled to theRF unit, and configured to receive device-to-device (D2D) resources usedfor transmission of D2D signals in radio resource control (RRC) idlemode, and transmit the D2D signals by using the D2D resources in the RRCidle mode.

In another aspect, a method for using, by a user equipment (UE),resources for a device-to-device (D2D) operation in a wirelesscommunication system is provided. The method includes receiving D2Dresources used for transmission of D2D signals in radio resource control(RRC) connected mode, and transmitting the D2D signals by using the D2Dresources in the RRC idle mode.

Advantageous Effects of Invention

D2D signals can be transmitted in RRC idle mode efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack and acontrol plane protocol stack of an LTE system.

FIG. 4 shows an example of a physical channel structure.

FIG. 5 and FIG. 6 show ProSe direct communication scenarios without arelay.

FIG. 7 shows reference architecture for ProSe.

FIG. 8 shows an example of one-step ProSe direct discovery procedure.

FIG. 9 shows an example of two-steps ProSe direct discovery procedure.

FIG. 10 shows an example of a method for transmitting D2D signalsaccording to an embodiment of the present invention.

FIG. 11 shows an example of a method for transmitting D2D signalsaccording to another embodiment of the present invention.

FIG. 12 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

MODE FOR THE INVENTION

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3^(rd)generation partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink LTE-advanced(LTE-A) is an evolution of the LTE.

For clarity, the following description will focus on LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There are one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC. Referring to FIG. 2, the eNB 20 may perform functions ofselection for gateway 30, routing toward the gateway 30 during a radioresource control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of broadcast channel (BCH)information, dynamic allocation of resources to the UEs 10 in both ULand DL, configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack and acontrol plane protocol stack of an LTE system. FIG. 3-(a) shows a blockdiagram of a user plane protocol stack of an LTE system, and FIG. 3-(b)shows a block diagram of a control plane protocol stack of an LTEsystem.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

FIG. 4 shows an example of a physical channel structure. A physicalchannel consists of a plurality of subframes in time domain and aplurality of subcarriers in frequency domain. One subframe consists of aplurality of symbols in the time domain. One subframe consists of aplurality of resource blocks (RBs). One RB consists of a plurality ofsymbols and a plurality of subcarriers. In addition, each subframe mayuse specific subcarriers of specific symbols of a corresponding subframefor a PDCCH. For example, a first symbol of the subframe may be used forthe PDCCH. The PDCCH carries dynamic allocated resources, such as aphysical resource block (PRB) and modulation and coding scheme (MCS). Atransmission time interval (TTI) which is a unit time for datatransmission may be equal to a length of one subframe. The length of onesubframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel. A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom a higher layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

Referring to FIG. 3-(a), the RLC and MAC layers (terminated in the eNBon the network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARQ). ThePDCP layer (terminated in the eNB on the network side) may perform theuser plane functions such as header compression, integrity protection,and ciphering.

Referring to FIG. 3-(b), the RLC and MAC layers (terminated in the eNBon the network side) may perform the same functions for the controlplane. The RRC layer (terminated in the eNB on the network side) mayperform functions such as broadcasting, paging, RRC connectionmanagement, RB control, mobility functions, and UE measurement reportingand controlling. The NAS control protocol (terminated in the MME ofgateway on the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC connected state and an RRC idlestate. When an RRC connection is established between the RRC layer ofthe UE and the RRC layer of the E-UTRAN, the UE is in RRC_CONNECTED, andotherwise the UE is in RRC_IDLE. Since the UE in RRC_CONNECTED has theRRC connection established with the E-UTRAN, the E-UTRAN may recognizethe existence of the UE in RRC_CONNECTED and may effectively control theUE. Meanwhile, the UE in RRC_IDLE may not be recognized by the E-UTRAN,and a CN manages the UE in unit of a TA which is a larger area than acell. That is, only the existence of the UE in RRC_IDLE is recognized inunit of a large area, and the UE must transition to RRC_CONNECTED toreceive a typical mobile communication service such as voice or datacommunication.

In RRC_IDLE state, the UE may receive broadcasts of system informationand paging information while the UE specifies a discontinuous reception(DRX) configured by NAS, and the UE has been allocated an identification(ID) which uniquely identifies the UE in a tracking area and may performpublic land mobile network (PLMN) selection and cell re-selection. Also,in RRC_IDLE state, no RRC context is stored in the eNB.

In RRC_CONNECTED state, the UE has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the eNB becomes possible. Also, the UE can report channelquality information and feedback information to the eNB. InRRC_CONNECTED state, the E-UTRAN knows the cell to which the UE belongs.Therefore, the network can transmit and/or receive data to/from UE, thenetwork can control mobility (handover and inter-radio accesstechnologies (RAT) cell change order to GSM EDGE radio access network(GERAN) with network assisted cell change (NACC)) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE specifies the paging DRX cycle. Specifically,the UE monitors a paging signal at a specific paging occasion of everyUE specific paging DRX cycle. The paging occasion is a time intervalduring which a paging signal is transmitted. The UE has its own pagingoccasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE moves from one TA to another TA, the UE willsend a tracking area update (TAU) message to the network to update itslocation.

When the user initially powers on the UE, the UE first searches for aproper cell and then remains in RRC_IDLE in the cell. When there is aneed to establish an RRC connection, the UE which remains in RRC_IDLEestablishes the RRC connection with the RRC of the E-UTRAN through anRRC connection procedure and then may transition to RRC_CONNECTED. TheUE which remains in RRC_IDLE may need to establish the RRC connectionwith the E-UTRAN when uplink data transmission is necessary due to auser's call attempt or the like or when there is a need to transmit aresponse message upon receiving a paging message from the E-UTRAN.

It is known that different cause values may be mapped o the signaturesequence used to transmit messages between a UE and eNB and that eitherchannel quality indicator (CQI) or path loss and cause or message sizeare candidates for inclusion in the initial preamble.

When a UE wishes to access the network and determines a message to betransmitted, the message may be linked to a purpose and a cause valuemay be determined. The size of the ideal message may be also bedetermined by identifying all optional information and differentalternative sizes, such as by removing optional information, or analternative scheduling request message may be used.

The UE acquires necessary information for the transmission of thepreamble, UL interference, pilot transmit power and requiredsignal-to-noise ratio (SNR) for the preamble detection at the receiveror combinations thereof. This information must allow the calculation ofthe initial transmit power of the preamble. It is beneficial to transmitthe UL message in the vicinity of the preamble from a frequency point ofview in order to ensure that the same channel is used for thetransmission of the message.

The UE should take into account the UL interference and the UL path lossin order to ensure that the network receives the preamble with a minimumSNR. The UL interference can be determined only in the eNB, andtherefore, must be broadcast by the eNB and received by the UE prior tothe transmission of the preamble. The UL path loss can be considered tobe similar to the DL path loss and can be estimated by the UE from thereceived RX signal strength when the transmit power of some pilotsequence of the cell is known to the UE.

The required UL SNR for the detection of the preamble would typicallydepend on the eNB configuration, such as a number of Rx antennas andreceiver performance. There may be advantages to transmit the ratherstatic transmit power of the pilot and the necessary UL SNR separatelyfrom the varying UL interference and possibly the power offset requiredbetween the preamble and the message.

The initial transmission power of the preamble can be roughly calculatedaccording to the following formula:

Transmit power=TransmitPilot−RxPilot+ULlnterference+Offset+SNRRequired

Therefore, any combination of SNRRequired, ULlnterference, TransmitPilotand Offset can be broadcast. In principle, only one value must bebroadcast. This is essentially in current UMTS systems, although the ULinterference in 3GPP LTE will mainly be neighboring cell interferencethat is probably more constant than in UMTS system.

The UE determines the initial UL transit power for the transmission ofthe preamble as explained above. The receiver in the eNB is able toestimate the absolute received power as well as the relative receivedpower compared to the interference in the cell. The eNB will consider apreamble detected if the received signal power compared to theinterference is above an eNB known threshold.

The UE performs power ramping in order to ensure that a UE can bedetected even if the initially estimated transmission power of thepreamble is not adequate. Another preamble will most likely betransmitted if no ACK or NACK is received by the UE before the nextrandom access attempt. The transmit power of the preamble can beincreased, and/or the preamble can be transmitted on a different ULfrequency in order to increase the probability of detection. Therefore,the actual transmit power of the preamble that will be detected does notnecessarily correspond to the initial transmit power of the preamble asinitially calculated by the UE.

The UE must determine the possible UL transport format. The transportformat, which may include MCS and a number of resource blocks thatshould be used by the UE, depends mainly on two parameters, specificallythe SNR at the eNB and the required size of the message to betransmitted.

In practice, a maximum UE message size, or payload, and a requiredminimum SNR correspond to each transport format. In UMTS, the UEdetermines before the transmission of the preamble whether a transportformat can be chosen for the transmission according to the estimatedinitial preamble transmit power, the required offset between preambleand the transport block, the maximum allowed or available UE transmitpower, a fixed offset and additional margin. The preamble in UMTS neednot contain any information regarding the transport format selected bythe EU since the network does not need to reserve time and frequencyresources and, therefore, the transport format is indicated togetherwith the transmitted message.

The eNB must be aware of the size of the message that the UE intends totransmit and the SNR achievable by the UE in order to select the correcttransport format upon reception of the preamble and then reserve thenecessary time and frequency resources. Therefore, the eNB cannotestimate the SNR achievable by the EU according to the received preamblebecause the UE transmit power compared to the maximum allowed orpossible UE transmit power is not known to the eNB, given that the UEwill most likely consider the measured path loss in the DL or someequivalent measure for the determination of the initial preambletransmission power.

The eNB could calculate a difference between the path loss estimated inthe DL compared and the path loss of the UL. However, this calculationis not possible if power ramping is used and the UE transmit power forthe preamble does not correspond to the initially calculated UE transmitpower. Furthermore, the precision of the actual UE transmit power andthe transmit power at which the UE is intended to transmit is very low.Therefore, it has been proposed to code the path loss or CQI estimationof the downlink and the message size or the cause value in the UL in thesignature.

Proximity Services (ProSe) are described. It may be refer to 3GPP TR23.703 V0.4.1 (2013-06). The ProSe may be a concept including adevice-to-device (D2D) communication. Hereinafter, the ProSe may be usedby being mixed with a device-to-device (D2D).

ProSe direct communication means a communication between two or more UEsin proximity that are ProSe-enabled, by means of user plane transmissionusing E-UTRA technology via a path not traversing any network node.ProSe-enabled UE means a UE that supports ProSe requirements andassociated procedures. Unless explicitly stated otherwise, aProSe-enabled UE refers both to a non-public safety UE and a publicsafety UE. ProSe-enabled public safety UE means a ProSe-enabled UE thatalso supports ProSe procedures and capabilities specific to publicsafety. ProSe-enabled non-public safety UE means a UE that supportsProSe procedures and but not capabilities specific to public safety.ProSe direct discovery means a procedure employed by a ProSe-enabled UEto discover other ProSe-enabled UEs in its vicinity by using only thecapabilities of the two UEs with 3GPP LTE rel-12 E-UTRA technology.EPC-level ProSe discovery means a process by which the EPC determinesthe proximity of two ProSe-enabled UEs and informs them of theirproximity.

When the registered public land mobile network (PLMN), ProSe directcommunication path and coverage status (in coverage or out of coverage)are considered, there are a number of different possible scenarios.Different combinations of direct data paths and in-coverage andout-of-coverage may be considered.

FIG. 5 and FIG. 6 show ProSe direct communication scenarios without arelay. FIG. 5-(a) shows a case that UE1 and UE2 are out of coverage.FIG. 5-(b) shows a case that UE1 is in coverage and in PLMN A, and UE2is out of coverage. FIG. 5-(c) shows a case that UE1 and UE2 are incoverage and in PLMN A, and UE1 and UE2 shares the same PLMN A and thesame cell. FIG. 5-(d) shows a case that UE1 and UE2 are in coverage andin the same PLMN A, but UE1 and UE2 are in different cells each other.FIG. 6-(a) shows a case that UE1 and UE2 are in coverage, but UE1 andUE2 are in different PLMNs (i.e., PLMN A/B) and different cells eachother. UE1 and UE2 are in both cells' coverage. FIG. 6-(b) shows a casethat UE1 and UE2 are in coverage, but UE1 and UE2 are in different PLMNs(i.e., PLMN A/B) and different cells each other. UE1 is in both cells'coverage and UE2 is in serving cell's coverage. FIG. 6-(c) shows a casethat UE1 and UE2 are in coverage, but UE1 and UE2 are in different PLMNs(i.e., PLMN A/B) and different cells each other. UE1 and UE2 are in itsown serving cell's coverage. In the description above, “in coverage andin PLMN A” means that the UE is camping on the cell of the PLMN A andunder the control of the PLMN A.

Two different modes for ProSe direct communication one-to-one may besupported.

-   -   Network independent direct communication: This mode of operation        for ProSe direct communication does not require any network        assistance to authorize the connection and communication is        performed by using only functionality and information local to        the UE. This mode is applicable only to pre-authorized        ProSe-enabled public safety UEs, regardless of whether the UEs        are served by E-UTRAN or not.    -   Network authorized direct communication: This mode of operation        for ProSe direct communication always requires network        assistance and may also be applicable when only one UE is        “served by E-UTRAN” for public safety UEs. For non-public safety        UEs both UEs must be “served by E-UTRAN”.

FIG. 7 shows reference architecture for ProSe. Referring to FIG. 7, thereference architecture for ProSe includes E-UTRAN, EPC, a plurality ofUEs having ProSe applications, ProSe application server, and ProSefunction. The EPC represents the E-UTRAN core network architecture. TheEPC may include entities such as MME, S-GW, P-GW, policy and chargingrules function (PCRF), home subscriber server (HSS), etc. The ProSeapplication servers are users of the ProSe capability for building theapplication functionality. In the public safety cases, they may bespecific agencies (PSAP), or in the commercial cases social media. Theseapplications may be defined outside the 3GPP architecture but there maybe reference points towards 3GPP entities. The application server cancommunicate towards an application in the UE. Applications in the UE usethe ProSe capability for building the application functionality. Examplemay be for communication between members of public safety groups or forsocial media application that requests to find buddies in proximity.

The ProSe function in the network (as part of EPS) defined by 3GPP has areference point towards the ProSe application server, towards the EPCand the UE. The functionality may include at least one of followings.But the functionality may not be restricted to the followings.

-   -   Interworking via a reference point towards the 3rd party        applications    -   Authorization and configuration of the UE for discovery and        direct communication    -   Enable the functionality of the EPC level ProSe discovery    -   ProSe related new subscriber data and handling of data storage,        and also handling of ProSe identities    -   Security related functionality    -   Provide control towards the EPC for policy related functionality    -   Provide functionality for charging (via or outside of EPC, e.g.,        offline charging) Reference points/interfaces in the reference        architecture for ProSe are described.    -   PC1: It is the reference point between the ProSe application in        the UE and in the ProSe application server. It is used to define        application level signaling requirements.    -   PC2: It is the reference point between the ProSe application        server and the ProSe function. It is used to define the        interaction between ProSe application server and ProSe        functionality provided by the 3GPP EPS via ProSe function. One        example may be for application data updates for a ProSe database        in the ProSe function. Another example may be data for use by        ProSe application server in interworking between 3GPP        functionality and application data, e.g., name translation.    -   PC3: It is the reference point between the UE and ProSe        function. It is used to define the interaction between UE and        ProSe function. An example may be to use for configuration for        ProSe discovery and communication.    -   PC4: It is the reference point between the EPC and ProSe        function. It is used to define the interaction between EPC and        ProSe function. Possible use cases may be when setting up a        one-to-one communication path between UEs or when validating        ProSe services (authorization) for session management or        mobility management in real time.    -   PC5: It is the reference point between UE to UE used for control        and user plane for discovery and communication, for relay and        one-to-one communication (between UEs directly and between UEs        over LTE-Uu).    -   PC6: This reference point may be used for functions such as        ProSe discovery between users subscribed to different PLMNs.    -   SGi: In addition to the relevant functions via SGi, it may be        used for application data and application level control        information exchange.

ProSe direct communication is a mode of communication whereby two publicsafety UEs can communicate with each other directly over the PC5interface. This communication mode is supported when the UE is served byE-UTRAN and when the UE is outside of E-UTRA coverage.

The ProSe-enabled UE may operate in two modes for resource allocation.In mode 1, resource allocation is scheduled by the eNB. In mode 1, theUE may need to be RRC_CONNECTED in order to transmit data. The UE mayrequest transmission resources from the eNB. The eNB may scheduletransmission resources for transmission of scheduling assignment(s) anddata. The UE may send a scheduling request (dedicated scheduling request(D-SR) or random access) to the eNB followed by a ProSe buffer statusreport (BSR). Based on the BSR, the eNB may determine that the UE hasdata for a ProSe direct communication transmission and estimate theresources needed for transmission. In mode, 2, a UE on its own selectsresources autonomously from resource pools to transmit schedulingassignment and data. If the UE is out of coverage, the UE may only usemode 2. If the UE is in coverage, the UE may use mode 1 or mode 2according to configuration of the eNB. When there are no exceptionalconditions, the UE may change from mode 1 to mode 2 or mode 2 to mode 1only if it is configured by the eNB. If the UE is in coverage, the UEshall use only the mode indicated by eNB configuration unless one of theexceptional cases occurs.

ProSe direct discovery is defined as the procedure used by theProSe-enabled UE to discover other ProSe-enabled UE(s) in its proximityusing E-UTRA direct radio signals via the PC5 interface. ProSe directdiscovery is supported only when the UE is served by E-UTRAN.

There are two types of resource allocation for discovery informationannouncement. Type 1 is a resource allocation procedure where resourcesfor announcing of discovery information are allocated on a non-UEspecific basis. The eNB may provide the UE(s) with the resource poolconfiguration used for announcing of discovery information. Theconfiguration may be signaled in system information block (SIB). The UEautonomously selects radio resource(s) from the indicated resource pooland announce discovery information. The UE may announce discoveryinformation on a randomly selected discovery resource during eachdiscovery period. Type 2 is a resource allocation procedure whereresources for announcing of discovery information are allocated on a perUE specific basis. The UE in RRC_CONNECTED may request resource(s) forannouncing of discovery information from the eNB via RRC. The eNB mayassign resource(s) via RRC. The resources may be allocated within theresource pool that is configured in UEs for monitoring.

FIG. 8 shows an example of one-step ProSe direct discovery procedure. InFIG. 8, two UEs are running the same ProSe-enabled application and it isassumed that the users of those UEs have a “friend” relationship on theconsidered application. The “3GPP Layers” shown in FIG. 8 correspond tothe functionality specified by 3GPP that enables mobile applications inthe UE to use ProSe discovery services.

UE-A and UE-B run a ProSe-enabled application, which discovers andconnects with an associated application server in the network. As anexample, this application could be a social networking application. Theapplication server could be operated by the 3GPP network operator or bya third-party service provider. When operated by a third-party provider,a service agreement is required between the third-party provider and the3GPP operator in order to enable communication between the ProSe Serverin the 3GPP network and the application server.

1. Regular application-layer communication takes place between themobile application in UE-A and the application server in the network.

2. The ProSe-enabled application in UE-A retrieves a list ofapplication-layer identifiers, called “friends”. Typically, suchidentifiers have the form of a network access identifier.

3. The ProSe-enabled application wants to be notified when one of UE-A'sfriends is in the vicinity of UE-A. For this purpose, it requests fromthe 3GPP layers to retrieve private expressions codes (i) for the userof UE-A (with an application-layer identity) and (ii) for each one ofhis friends.

4. The 3GPP layers delegate the request to a ProSe server in the 3GPPnetwork. This server can be located either in home PLMN (HPLMN) or in avisited PLMN (VPLMN). Any ProSe server that supports the consideredapplication can be used. The communication between the UE and ProSeserver can take place either over the IP layer or below the IP layer. Ifthe application or the UE is not authorized to use ProSe discovery, thenthe ProSe server rejects the request.

5. The ProSe server maps all provided application-layer identities toprivate expression codes. For example, the application-layer identity ismapped to the private expression code. This mapping is based onparameters retrieved from the application server in the network (e.g.,mapping algorithm, keys, etc.) thus the derived private expression codecan be globally unique. In other words, any ProSe server requested toderive the private expression of the application-layer identity for aspecific application, it will derive the same private expression code.The mapping parameters retrieved from the application server describehow the mapping should be done. In this step, the ProSe server and/orthe application server in the network authorize also the request toretrieve expression codes for a certain application and from a certainuser. It is ensured, for example, that a user can retrieves expressioncodes only for his friends.

6. The derived expression codes for all requested identities are sent tothe 3GPP layers, where they are stored for further use. In addition, the3GPP layers notify the ProSe-enabled application that expression codesfor the requested identities and application have been successfullyretrieved. However, the retrieved expression codes are not sent to theProSe-enabled application.

7. The ProSe-enabled application requests from the 3GPP layers to startdiscovery, i.e., attempt to discover when one of the provided “friends”is in the vicinity of UE-A and, thus, direct communication is feasible.As a response, UE-A announces the expression code of theapplication-layer identity for the considered application. The mappingof this expression code to the corresponding application-layer identifycan only be performed by the friends of UE-A, who have also received theexpression codes for the considered application.

8. UE-B also runs the same ProSe-enabled application and has executedsteps 3-6 to retrieve the expression codes for friends. In addition, the3GPP layers in UE-B carry out ProSe discovery after being requested bythe ProSe-enabled application.

9. When UE-B receives the ProSe announcement from UE-A, it determinesthat the announced expression code is known and maps to a certainapplication and to the application-layer identity. The UE-B candetermine the application and the application identity that correspondsto the received expression code because it has also received theexpression code for the application-layer identity (UE-A is included inthe friend list of UE-B).

The steps 1-6 in the above procedure can only be executed when the UE isinside the network coverage. However, these steps are not requiredfrequently. They are only required when the UE wants to update or modifythe friends that should be discovered with ProSe direct discovery. Afterreceiving the requested expression codes from the network, the ProSediscovery (steps 7 and 9) can be conducted either inside or outside thenetwork coverage.

It is noted that an expression code maps to a certain application and toa certain application identity. Thus when a user runs the sameProSe-enabled application on multiple UEs, each UE announces the sameexpression code.

FIG. 9 shows an example of two-steps ProSe direct discovery procedure.

1. The user of UE1 (the discoverer) wishes to discover whether there areany members of a specific group communication service enabler (GCSE)group in proximity. UE1 broadcasts a targeted discovery request messagecontaining the unique App group ID (or the Layer-2 group ID) of thetargeted GCSE group. The targeted discovery request message may alsoinclude the discoverer's unique identifier (App personal ID of user 1).The targeted discovery request message is received by UE2, UE3, UE4 andUE5. Apart from the user of UE5, all other users are members of therequested GCSE group and their UEs are configured accordingly.

2a-2c. Each one of UE2, UE3 and UE4 responds directly to UE1 with atargeted discovery response message which may contain the unique Apppersonal ID of its user. In contrast, UE5 sends no response message.

In three step procedure, UE1 may respond to the targeted discoveryresponse message by sending a discovery confirm message.

It has been discussed that D2D signals can be transmitted in RRC_IDLE aswell as RRC_CONNECTED. For transmission of D2D signals in RRC_IDLE,radio resources for D2D signals in RRC_IDLE may be newly defined.Accordingly, a method for controlling a D2D operation based on RRC stateand/or a method for controlling applicability of D2D resources accordingto RRC state may be required.

According to an embodiment of the present invention, the network mayconfigure D2D resources to the UE. The network may configure the UE withRRC state or RRC state related information that determines in which RRCstate the corresponding D2D resources are applicable, and accordingly,the UE may determine whether resource information for a D2D operationobtained in one RRC state is applicable in another RRC state as well orin which RRC state the obtained radio resource is applicable (i.e., inwhich RRC state the UE is allowed to perform D2D transmission). That is,the network may configure D2D resources to the UE, and the configuredD2D resources and using the configured D2D resources may be valid andrestricted in a specific RRC state. The configured D2D resources may beused only in the corresponding RRC state. The D2D operation of the UEmay be determined according to the validity of the D2D resources.Hereinafter, the D2D signals may include at least one of a D2D discoverysignal/message or a D2D communication data.

FIG. 10 shows an example of a method for transmitting D2D signalsaccording to an embodiment of the present invention. In step S100, theUE receives D2D resources used for transmission of D2D signals inRRC_IDLE. In step S110, the UE transmits the D2D signals by using theD2D resources in RRC_IDLE. Various cases for validity and/orapplicability of D2D resources, which is configured in RRC_IDLE,according to an RRC state may be considered.

(1) The network may configure D2D resources in RRC_IDLE via broadcastsignaling, and the configured D2D resource may be valid only inRRC_IDLE. The UE performs a D2D operation in RRC_IDLE by using theconfigured D2D resources, but when the UE enters RRC_CONNECTED, theconfigured D2D resource may be considered invalid in RRC_CONNECTED. TheUE for which transmission of D2D signals allowed only in RRC_CONNECTEDmay consider that it is allowed to perform transmission of D2D signalsonly after D2D resources are dedicatedly allocated to the UE by thenetwork. Accordingly, the UE may transmit D2D signals only in RRC_IDLEby using the configured D2D resources in RRC_IDLE. The UE may receiveD2D signals only in RRC_IDLE by using the configured D2D resources inRRC_IDLE. The broadcast signaling may be system information,specifically a system information block type 18 (SIB18) which is newlydefined for D2D resources.

Further, the applicability of the D2D resources configured in RRC_IDLEmay be further restricted. For example, the D2D resources configured inRRC_IDLE may be only applicable in RRC_IDLE under specific conditions.The specific condition may be predefined condition or the network mayconfigure the specific condition. The predefined condition may includethe case where the UE cannot enter RRC_CONNECTED due to failure of theRRC connection establishment. The predefined condition may also includethe case where the UE afterwards enter RRC_IDLE due to failure ofkeeping RRC_CONNECTED (e.g., radio link failure).

For example, the UE may receive D2D resources for autonomoustransmission of D2D signals in RRC_IDLE, and may use the D2D resourcesonly in RRC_IDLE. The received D2D resources may be considered invalidin RRC_CONNECTED. The D2D resources for autonomous transmission of D2Dsignals may be type 1 autonomous transmission resource pool for D2Ddiscovery described above. That is, the D2D resources for autonomoustransmission of D2D signals may be resources for announcing of discoveryinformation allocated on a non-UE specific basis. Or, the D2D resourcesfor autonomous transmission of D2D signals may be mode 2 autonomoustransmission resource pool for D2D communication described above. Thatis, the D2D resources for autonomous transmission of D2D signals may beresources from which a UE on its own selects resources.

(2) The network may configure D2D resources in RRC_IDLE via broadcastsignaling, and the configured D2D resource may be valid in both RRC_IDLEand RRC_CONNECTED. The UE performs a D2D operation in RRC_IDLE by usingthe configured D2D resources, an even after when the UE entersRRC_CONNECTED, the configured D2D resource may be considered valid inRRC_CONNECTED. In this case, the D2D resources may be considered validin RRC_CONNECTED until the UE receives an RRC connection reconfigurationmessage. Accordingly, the UE may transmit D2D signals in both RRC_IDLEand RRC_CONNECTED by using the configured D2D resources in RRC_IDLE. TheUE may receive D2D signals in both RRC_IDLE and RRC_CONNECTED by usingthe configured D2D resources in RRC_IDLE. The broadcast signaling may besystem information, specifically a SIB18.

After receiving the RRC connection reconfiguration message, the UE mayperform a D2D operation according to a configuration in the RRCconnection reconfiguration message. If the RRC connectionreconfiguration message includes dedicated D2D resources, the UEperforms a D2D operation according to the dedicated D2D resources. Ifthe RRC connection reconfiguration message does not include anydedicated D2D resources, the UE may stop a D2D operation. Alternatively,if the RRC connection reconfiguration message does not include anydedicated D2D resources but the RRC connection reconfiguration messageindicates that UE can continue to use the D2D resources that areavailable before receiving the RRC connection reconfiguration message,the UE may continue to use the D2D resources for performing a D2Doperation.

(3) The network may configure D2D resources in RRC_IDLE via broadcastsignaling, and the configured D2D resource may be valid only inRRC_CONNECTED. This case may not be covered by the embodiment describedin FIG. 10. When the UE enters RRC_CONNECTED, the configured D2Dresource may be considered valid in RRC_CONNECTED. Accordingly, if theD2D resources are resources for D2D transmission, the UE may transmitD2D signals only in RRC_CONNECTED by using the D2D resources configuredin RRC_IDLE. If the D2D resources are resources for D2D reception, theUE may receive D2D signals only in RRC_CONNECTED by using the D2Dresources configured in RRC_IDLE. The broadcast signaling may be systeminformation, specifically a SIB18.

Further, the applicability of the D2D resources, which are signaled inRRC_IDLE but applicable in RRC_CONNECTED, may be further restricted. Forexample, the D2D resources configured in RRC_IDLE may be only applicablein RRC_CONNECTED under specific conditions. The specific condition maybe predefined condition or the network may configure the specificcondition. The predefined condition may include the case where the UEconsiders that the current RRC connection is problematic. The UE mayconsider that the current RRC connection is problematic when radio linkfailure happens or when physical layer problem happens.

Further, the applicability of the D2D resources, which are signaled inRRC_IDLE but applicable in RRC_CONNECTED, may be further restricted. Forexample, the D2D resources configured in RRC_IDLE may become applicableonly if the network configures the UE to use the D2D resources viadedicated signaling. The network may configure the UE to use the D2Dresources during the RRC connection establishment procedure or RRCconnection reconfiguration procedure. A simple indication (e.g., one bitindicator) may be used for that configuration.

FIG. 11 shows an example of a method for transmitting D2D signalsaccording to another embodiment of the present invention. In step S200,the UE receives D2D resources used for transmission of D2D signals inRRC_CONNECTED. In step S110, the UE transmits the D2D signals by usingthe D2D resources in RRC_IDLE. Various cases for validity and/orapplicability of D2D resources, which is configured in RRC_CONNECTED,according to an RRC state may be considered.

(1) The network may configure D2D resources in RRC_CONNECTED viadedicated signaling, and the configured D2D resource may be valid onlyin RRC_IDLE. The network may configure D2D resources in RRC_CONNECTEDvia an RRC connection reconfiguration message, and may indicate the UEthat the configured D2D resources are valid only in RRC_IDLE.Alternatively, the network may configure D2D resources in RRC_CONNECTEDvia an RRC connection release message, and the configured D2D resourcesmay be used in RRC_IDLE. Accordingly, the UE may transmit D2D signalsonly in RRC_IDLE by using the configured D2D resources in RRC_CONNECTED.The UE may receive D2D signals only in RRC_IDLE by using the configuredD2D resources in RRC_CONNECTED. The dedicated signaling may included anexplicit indication, e.g., RRC state flag, which indicates that theconfigured D2D resources are valid in both RRC_IDLE and RRC_CONNECTED.Or, the dedicated signaling itself may function as an implicitindication which indicates that the configured D2D resources are validin both RRC_IDLE and RRC_CONNECTED. The RRC connection reconfigurationmessage or the RRC connection release message are just examples of astate transition message, and the present invention is not limitedthereto.

(2) The network may configure D2D resources in RRC_CONNECTED viadedicated signaling, and the configured D2D resource may be valid inboth RRC_IDLE and RRC_CONNECTED. The network may configure D2D resourcesin RRC_CONNECTED via an RRC connection reconfiguration message, and mayindicate the UE that the configured D2D resources are valid in bothRRC_IDLE and RRC_CONNECTED. Accordingly, the UE may transmit D2D signalsin both RRC_IDLE and RRC_CONNECTED by using the configured D2D resourcesin RRC_CONNECTED. The UE may receive D2D signals in both RRC_IDLE andRRC_CONNECTED by using the configured D2D resources in RRC_CONNECTED.

For example, the UE may receive D2D resources for autonomoustransmission of D2D signals in RRC_CONNECTED, and may use the D2Dresources in both RRC_CONNECTED and RRC_IDLE. The D2D resources forautonomous transmission of D2D signals may be type 1 autonomoustransmission resource pool for D2D discovery described above. That is,the D2D resources for autonomous transmission of D2D signals may beresources for announcing of discovery information allocated on a non-UEspecific basis. Or, the D2D resources for autonomous transmission of D2Dsignals may be mode 2 autonomous transmission resource pool for D2Dcommunication described above. That is, the D2D resources for autonomoustransmission of D2D signals may be resources from which a UE on its ownselects resources.

The network may configure D2D resources in RRC_CONNECTED via dedicatedsignaling with a validity timer. The validity timer may start when theD2D resources are received. The validity timer may continue to run whenthe UE enters RRC_IDLE. The D2D resources may be considered valid onlywhile the validity timer is running. When validity timer expires, the UEmay discard the D2D resources as a resource that is applicable inRRC_IDLE. Or, the validity timer may start when state transition occursafter receiving the D2D resources. If the validity timer value is notprovided, the D2D resources may be considered valid only for the firstcoming RRC_IDLE once the UE receives the D2D resources. Once the UEenters RRC_CONNECTED, the UE may discard the D2D resources as a resourcethat is applicable in RRC_IDLE.

For example, the UE may receive D2D resources, scheduled by the network,in RRC_CONNECTED, and may use the D2D resources in both RRC_CONNECTEDand RRC_IDLE. In RRC_IDLE, the D2D resources may be used for specificduration indicated by the validity timer. The D2D resources scheduled bythe network may be type 2 scheduled transmission resource pool for D2Ddiscovery described above. That is, the D2D resources scheduled by thenetwork may be resources for announcing of discovery informationallocated on a per UE specific basis. Or, the D2D resources scheduled bythe network may be mode 1 scheduled transmission resource pool for D2Dcommunication described above.

Alternatively, the network may configure the UE whether the UE isallowed to use resource reserved/allowed or known for transmission ofD2D signals in both RRC_IDLE and RRC_CONNECTED or only in RRC_CONNECTED.Then, if the network configure the UE such that the UE is not allowed touse resource reserved/allowed or known for transmission of D2D signalsin RRC_IDLE, the UE considers that transmission of D2D signals is notallowed in RRC_IDLE even if the UE knows resources reserved/known fortransmission of D2D signals, and the UE considers that transmission ofD2D signals is only allowed while in RRC_CONNECTED.

Hereinafter, a method for handling of D2D resources upon RRC statetransition according to an embodiment of the present invention isdescribed. It is possible that upon RRC state transition, the D2Dresources are considered invalid (i.e., unusable), and the UE maysuspend using D2D resources for a D2D operation. For the UE attemptingRRC state transition from RRC_IDLE to RRC_CONNECTED and the UE was usingD2D resources in RRC_IDLE, the UE may consider D2D resources invalidonce the UE starts RRC connection establishment procedure. This maycorrespond to the embodiment described in FIG. 10. The initiation of RRCconnection establishment may be defined by sending RACH preamble.

Once the resource is discarded (i.e., considered invalid), the UE mayconsider discarded D2D resources valid again. The UE may considerdiscarded D2D resources valid under various conditions described asfollows.

-   -   The UE may consider invalid D2D resources valid if connection        establishment is successfully completed.    -   The UE may consider invalid D2D resources valid if connection        establishment is successfully completed and the cell indicates,        during RRC connection establishment procedure (e.g., in RRC        connection setup message), that the UE is allowed to consider        the discarded D2D resources valid.    -   The UE may consider invalid D2D resources valid if connection        establishment is successfully completed and then first        reconfiguration procedure is successfully completed.    -   The UE may consider invalid D2D resources valid if connection        establishment is successfully completed and then first        reconfiguration procedure is successfully completed and the cell        indicates, during RRC connection reconfiguration procedure        (e.g., in RRC connection reconfiguration message), that the UE        is allowed to consider the discarded D2D resources valid.

For the UE attempting RRC state transition from RRC_CONNECTED toRRC_IDLE and the UE was using D2D resources in RRC_CONNECTED, variouscases may be considered described as follows.

-   -   Once the UE enters RRC_IDLE, the UE may discard the D2D        resources used in RRC_CONNECTED by default.    -   Once the UE enters RRC_IDLE, the UE may discard the D2D        resources if the network transmits an RRC connection release        message including discard of D2D resources.    -   Once the UE enters RRC_IDLE, the UE may not discard the D2D        resources, i.e., using D2D resources used in RRC_CONNECTED also        in RRC_IDLE as well. This may correspond to the embodiment        described in FIG. 11.    -   Once the UE enters RRC_IDLE, the UE may not discard the D2D        resources if the network transmits an RRC connection release        message including continuation of using D2D resources, i.e.,        using D2D resources used in RRC_CONNECTED also in RRC_IDLE as        well. This may also correspond to the embodiment described in        FIG. 11.    -   Once the UE enters RRC_IDLE, the UE may not discard the D2D        resources if the network transmits an RRC connection release        message including D2D resources that can be used in RRC_IDLE.        This may also correspond to the embodiment described in FIG. 11.    -   Once the UE enters RRC_IDLE, the UE may discard the D2D        resources if the D2D resources that were used by the UE in        RRC_CONNECTED are not subset of D2D resources that can be used        in RRC_IDLE. The UE may identify this condition by referring to        D2D resources for RRC_IDLE as indicated in system information        and D2D resources for RRC_CONNECTED as indicted by system        information or dedicated signaling.    -   Once the UE enters RRC_IDLE, the UE may discard only the D2D        resources that were used by the UE in RRC_CONNECTED but are not        overlapped with D2D resources that can be used in RRC_IDLE. So        UE may continue to use D2D resources that were used by the UE in        RRC_CONNECTED and are overlapped with D2D resources that can be        used in RRC_IDLE. The UE may identify this condition by        referring to D2D resources for RRC_IDLE as indicated in system        information and D2D resources for RRC_CONNECTED as indicted by        system information or dedicated signaling.

Upon discarding the D2D resources, the UE may suspend both D2Dtransmission using the D2D resources and reception using the D2Dresources. Alternatively, the UE may only suspend D2D transmission usingthe D2D resources but continues reception using D2D resources. If thediscarded D2D resources are considered valid again, the UE may resumesuspended D2D operation.

When the UE detects that there are not the D2D resources applicable, theUE may indicate this to the upper layer that is responsible for a D2Dservice. The upper layer may be a layer which is in charge of schedulingor resource allocation, or in charge of overall UE proximity service, orapplication layer that can manage overall D2D service. When the UEdetects that there are D2D resources applicable, the UE may indicatethis to the upper layer that is responsible for D2D resource.

FIG. 12 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

An entity of the network 800 may include a processor 810, a memory 820and a radio frequency (RF) unit 830. The processor 810 may be configuredto implement proposed functions, procedures and/or methods described inthis description. Layers of the radio interface protocol may beimplemented in the processor 810. The memory 820 is operatively coupledwith the processor 810 and stores a variety of information to operatethe processor 810. The RF unit 830 is operatively coupled with theprocessor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The RF unit 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

1. A method for using, by a user equipment (UE), resources for adevice-to-device (D2D) operation in a wireless communication system, themethod comprising: receiving D2D resources used for transmission of D2Dsignals in radio resource control (RRC) idle mode; and transmitting theD2D signals by using the D2D resources in the RRC idle mode.
 2. Themethod of claim 1, wherein the D2D resources are configured via systeminformation.
 3. The method of claim 2, wherein the system information isa system information block type-18.
 4. The method of claim 1, whereinthe D2D resources are used in the RRC idle mode only.
 5. The method ofclaim 1, further comprising: transmitting the D2D signals by using theD2D resources after entering the RRC connected mode.
 6. The method ofclaim 5, wherein the D2D resources are used in the RRC connected modeuntil receiving an RRC connection reconfiguration message.
 7. The methodof claim 1, wherein the D2D signals include at least one of a D2Ddiscovery signal or a D2D communication data.
 8. A user equipment (UE)in a wireless communication system, the UE comprising: a radio frequency(RF) unit for transmitting or receiving a radio signal; and a processorcoupled to the RF unit, and configured to: receive device-to-device(D2D) resources used for transmission of D2D signals in radio resourcecontrol (RRC) idle mode; and transmit the D2D signals by using the D2Dresources in the RRC idle mode.
 9. A method for using, by a userequipment (UE), resources for a device-to-device (D2D) operation in awireless communication system, the method comprising: receiving D2Dresources used for transmission of D2D signals in radio resource control(RRC) connected mode; and transmitting the D2D signals by using the D2Dresources in the RRC idle mode.
 10. The method of claim 9, wherein theD2D resources are configured via a dedicated signaling.
 11. The methodof claim 10, wherein the dedicated signaling includes an RRC connectionreconfiguration message or an RRC connection release message.
 12. Themethod of claim 9, wherein the D2D resources are used in the RRC idlemode only.
 13. The method of claim 9, further comprising: transmittingthe D2D signals by using the D2D resources in the RRC connected mode.14. The method of claim 13, further comprising: receiving an indicationwhich indicates that the D2D resources are used in both the RRC idlemode and the RRC connected mode.
 15. The method of claim 9, wherein theD2D signals include at least one of a D2D discovery signal or a D2Dcommunication data.